Compton Scattering at HIGS Compton Scattering at HIGS
with Polarized Photonswith Polarized Photons
George Washington UniversityGeorge Washington University Jerry FeldmanJerry Feldman Mark SikoraMark Sikora
Duke University/TUNL Luke Myers Luke Myers Henry Weller Mohammad Ahmed Jonathan Mueller Seth Henshaw
Compton@HIGS CollaborationCompton@HIGS Collaboration
University of Kentucky Mike Kovash
Outline
What (and where) is HIGS?What (and where) is HIGS?
What have we done so far at HIGS?What have we done so far at HIGS? polarized Compton scattering study of IVGQR
elastic Compton scattering on 6Li high energy (60-86 MeV) and low energy (3-5 MeV)
What are we planning to do at HIGS?What are we planning to do at HIGS? elastic Compton scattering on deuterium
neutron polarizability
polarized Compton scattering on proton proton electric polarizability
double-polarized Compton scattering on proton proton spin polarizability
Background Background
Information on Information on
HIGSHIGS
United States
North Carolina
Duke University
TUNLHIGSHIGS
TUNLTUNLTriangle Universities Nuclear Laboratory
Duke Free-Electron Laser Lab
Storage Ring and Booster
Circularly and linearly polarized Circularly and linearly polarized rays, nearly rays, nearly monoenergeticmonoenergetic ( (EE 2 2––90 MeV) 90 MeV)
Utilizes Compton backscattering to generate Utilizes Compton backscattering to generate raysrays
Booster InjectorBooster Injector
LINACLINAC
RF CavityRF Cavity
MirrorMirror
Optical KlystronOptical Klystron
FELFEL
HIGS Photon Beam
to target room
HIGS Photon Beam
monoenergetic photons up to ~90 MeV energy will reach ~160 MeV by 2015
100% linear or circular polarization
high photon beam intensity ~107 Hz at 20-60 MeV
~108 Hz below 15 MeV
low beam-related background no bremsstrahlung typical of tagged photons
Polarized Compton ScatteringPolarized Compton Scattering
for IVGQR Systematicsfor IVGQR Systematics
Giant Resonances
L = 1
L = 2
T = 0 T = 1 collective nuclear excitations
GDR and ISGQR well known
IVGQR poorly knownIVGQR poorly known
photon as isovectorisovector probe
use pol. photons for IVGQRuse pol. photons for IVGQR
map systematics vs. A
nuclear symmetry energy neutron star eqn. of state
• ratio of H/V scattered photons is sensitive to ratio of H/V scattered photons is sensitive to E1/E2 interferenceE1/E2 interference
• sign difference in interference term at forward/backward anglessign difference in interference term at forward/backward angles
Photon Asymmetry in IVGQR
pure E1 E1/E2 interference
HINDA Array HIHIGS NNaI DDetector AArray
55o 55o
125o
125o
209Bi
Results for 209Bi
Results for 89Y
measured measured 124124Sn last month!Sn last month!
lease 142Nd target from ORNL for $15k
other targets include A ~ 56, 180, 238
extend measurements to extend measurements to 8989YY
%18%110
88.123.8
2.07.270
S
E
EWSR
MeV
MeV
89Y
preliminary
Results for 124Sn
IVGQR Systematics
89Y
209Bi
Pitthan 1980
124Sn
Compton Scattering Compton Scattering
on on 66LiLi
World Data Set
D(,)D
Lucas – Illinois (1994)Lucas – Illinois (1994)EE = 49, 69 MeV = 49, 69 MeV
Hornidge – SAL (2000)Hornidge – SAL (2000)EE = 85-105 MeV = 85-105 MeV
Lundin – Lund (2003)Lundin – Lund (2003)EE = 55, 66 MeV = 55, 66 MeV
Myers and ShonyozovMyers and Shonyozov (coming 2013)(coming 2013)Illinois, GW, UK, LundIllinois, GW, UK, Lund
EE = 58-115 MeV = 58-115 MeV
EFT Fits to Deuteron Data
LundinLundinLucasLucas
Lucas, LundinLucas, Lundin HornidgeHornidge
Griesshammer 2012
Summary of Neutron Results
Neutron scattering Schmiedmayer (91) n = 12.6 1.5(stat)
2.0(syst) Quasi-free Compton scattering
Kossert (03) n = 12.5 1.8(stat) (syst) 1.1(model)+1.1
–0.6
n = 2.7 1.8(stat) (syst) 1.1(model)+0.6–1.1
Elastic Compton scattering data from Lucas (94), Hornidge (00), Lundin (03)
n = 11.6 1.5 (stat) 0.6 (Baldin)
n = 3.6 1.5 (stat) 0.6 (Baldin)
Hildebrandt 05
n = 11.1 1.8 (stat) 0.4 (Baldin) 0.8 (theory)n = 4.1 1.8 (stat) 0.4 (Baldin) (0.8 (theory)
Griesshammer 12
Experiment on 6Li at HIGS
energies: EE = 60, 86 MeV = 60, 86 MeV
angles: = 40°-160° = 40°-160° ( = 17°)
target: solid 12.7 cm long 12.7 cm long 66LiLi cylinder (plus empty)
detectors: eight 10”eight 10”12” NaI’s12” NaI’s (HINDA array) good photon energy resolution (E/E < 5%)
experiment motivation exploit higher nuclear cross section to measure and
cross section scales as Z2, so factor of 9x higher than 2H
solid 6Li target is simple provided by Univ. of Saskatchewan
no previous Compton data on 6Li exists (except Pugh 1957)
HINDA Array HIHIGS NNaI DDetector AArray
Experimental Setup
Sample Spectra
6Li(,)6Li E = 60 MeV
Full and Empty Targets Full Empty subtraction
Cross Section for 16O(,)16O
Cross Section for 6Li(,)6Li
sum rule: + = 14.5
L. Myers et al.Phys. Rev. C86(2012)
E = 60 MeV
(, ) = (10.9, 3.6)
= 2 = 2
sum rule: + = 14.5
EE = 60 MeV = 60 MeV
7.4%
EE = 80 MeV = 80 MeV
12.8%
EE = 100 MeV = 100 MeV
20.9%
E = 86 MeV
Cross Section for 6Li(,)6Li
preliminary
Bampa 2011
Lundin (Lund) – 55 MeVLucas (Illinois) – 49 MeVLucas (Illinois) – 49 MeV
D(D(,,)D)D
LIT Method for Compton Scattering
Nuclear Polarizability Nuclear Polarizability
of of 66Li (and Li (and 44He?)He?)
Nuclear Polarizability
nuclear polarizability affects energy levels of light atoms non-negligible corrections for high-precision tests of QED
extraction of nuclear quantities from atomic spectroscopy nuclear charge radius from Lamb shift in muonic atoms
usually determined from photoabsorption sum rule
Nuclear Polarizability of 6Li
E = 0.163 0.064
M = 0.018 0.012
E = 3.0 MeV
6Li(,)6Li
= 55 = 90
= 55 = 0 = 125 = 0
= 125 = 90
E = 4.2 MeV
6Li(,)6Li
= 55 = 90
= 55 = 0 = 125 = 0
= 125 = 90
Compton ScatteringCompton Scattering
on the on the
Proton and DeuteronProton and Deuteron
Compton Scattering on Deuterium
unpolarized photon beam and unpolarized deuterium target
first use of our new LD2 cryogenic target
scattering angles 45o, 80o, 115o, 150o (E = 65, 100 MeV)
requires 300 hrs (65 MeV) + 100 hrs (100 MeV)
detectors: eight 10”12” NaI’s (HINDA array) arranged symmetrically left/right
LHLH22/LD/LD
22/LHe/LHe
Cryogenic Target
paid by GWU and TUNL
procured from vendors
assembled at HIGS
first run Oct. 2013?
(3.5 K 24 K)
HINDA Array HIHIGS NNaI DDetector AArray
55o
125o
55o
125o
Sum-Rule-Independent Measurement of p
linearly polarized linearly polarized photon beam (unpolarized target) scintillating active target (detect recoils in coincidence)
measure scattered photons at 90measure scattered photons at 90oo (E = 82 MeV)
scattering cross section is independent of p
extraction of p is independent of the Baldin sum rule
extraction of p is model-independent
requires 300 hrs for 5% uncertainty in p
detectors: four 10”12” NaI’s (HINDA array) located left, right, up, down
Sum-Rule-Independent Measurement of p
(point)
(point)
Polarizability of the Proton
Scintillating Target
simulations: R. Miskimen
Nucleon Spin Polarizability
forward and backward spin polarizabilities
Polarization Observables
xy
z
k
k
d
RCP (+)
LCP ()
Circular polarization
Circular polarization
Linear polarization
z2
x2
||
||
3
Spin Polarizabilities of the Proton
measure 2x for first determination of proton first determination of proton E1E1E1E1
circularly polarized photon beam scintillating active transversetransverse polarized target (P ~ 80%)
scattering angles 65o, 90o, 115o (E = 100 MeV)
requires 800 hrs for E1E1 = 1
detectors: eight 10”12” NaI’s 4 in plane, 4 out of plane
Circular polarization
x2
Spin Polarizabilities of the Proton
expandexpand
simulations: R. Miskimen
Summary
Early measurements of Compton scattering at HIGSEarly measurements of Compton scattering at HIGS polarized A(,)A for A = 89-209 (IVGQR systematics)
6Li(,)6Li at 60, 86 MeV (nucleon polarizability)
polarized 6Li(,)6Li at 3.0-4.2 MeV (nuclear polarizability)
Next generation of experiments on light nucleiNext generation of experiments on light nuclei D(,)D at 65 and 100 MeV (neutron polarizability)
polarizedpolarized p(,)p at 82 MeV (proton electric polarizability)
polarizedpolarized 4He(,)4He at 3-15 MeV (nuclear polarizability)
double-polarizeddouble-polarized Compton scattering on proton/deuteron nucleon spin polarizability
HIGS can contribute high-quality polarized data!HIGS can contribute high-quality polarized data! stay tuned for further developments in the future…
Extra slides
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Phenomenological Formalism
Cross-Section Ratios for Deuterium
N = 1
Level Scheme of 6Li
Nuclear Polarizability
Calculations by Trento Group
Bacca 2002
photoabsorption on 6Li• Lorentz Integral Transform method• extend calculations to case of Compton scattering
NaI Detectors
Pb collimator
Paraffin n shield 10" 10" NaI core detector
3" thick optically isolated NaI shield segments (8 in total)
E = 3.0 MeV
E = 4.2 MeV
= 55
= 55 = 125
= 125
Nuclear Polarizability of 4He
E = 0.061 0.007 (stat) 0.020 (syst)
M = 0.007 0.001 (stat) 0.002 (syst)
Nuclear Polarizability of 4He
E = 0.061 0.007 (stat) 0.020 (syst)
M = 0.007 0.001 (stat) 0.002 (syst)
Compton Scattering with scintillating targetLig
ht
Ou
tpu
t
Missing Energy (MeV)
deuteron proton
simulations: R. Miskimen
Nucleon Spin Polarizability
classical analogy: Faraday rotation of linearly polarized
light in a spin-polarized medium
four spin polarizabilities: 1, …,4
forward spin polarizability: 0 = 1 – 2 – 24
backward spin polarizability: = 1 + 2 + 24
expt. asymmetries with circularly polarized photons x : target spin photon helicity (in reaction plane)
z : target spin parallel to photon helicity